1. Field of the Invention
This invention relates to a recording material such as a pressure-sensitive material, a heat-sensitive material and a light-sensitive material, and more particularly to a recording material containing a leuco dye.
2. Description of the Prior Art
In various recording materials including pressure-sensitive, heat-sensitive and light-sensitive materials, a leuco dye is frequently used as a color image forming substance. The leuco dye, which is also referred to as a redox dye, develops a color on contact with an acid color developer.
The leuco dye is generally contained in microcapsules which are dispersed in a recording material. In an image forming process, the microcapsules are broken by external energy such as pressure and/or heat so that the dye comes into contact with acid color developer which has been arranged outside of the microcapsules in the recording material.
A conventional leuco dye which develops a bluish color is a phthalide compound such as 3,3-bis(p-dimethylaminophenyl)-6-dimethyl-aminophthalide (Crystal Violet Lactone), which develops deep bluish purple color. Crystal Violet Lactone can rapidly develop the color. However, Crystal Violet Lactone does not satisfy the requirement with respect to light fastness, that is, the developed color tends to fade from the image when it is irradiated with light. Other examples of the leuco dye which develops a bluish color are described in Japanese Patent Publication No. 56(1981)-11594 (corresponding to U.S. Pat. Nos. 3,930,671) and Japanese Patent Provisional Publication Nos. 51(1976)-121035 (corresponding to U.S. patent application Ser. No. 566,851) and 51(1976)-121036 (corresponding to U.S. patent application Ser. No. 566,854).